Laser flash photolysis study of the photochemical formation of colloidal Ag nanoparticles in the presence of benzophenone

Sensitized photoreduction of Ag+ ions and subsequent formation of colloidal Ag nanoparticles take place when an aqueous solution of a mixture of AgClO4, sodium dodecylsulfate (SDS) and benzophenone (BP) is irradiated with near-UV light. In this study, the mechanism and kinetics of the reaction have been studied by means of nanosecond laser flash photolysis, time-resolved emission spectroscopy and also steady-state photolysis. Benzophenone ketyl radial (BPK) is formed by the hydrogen abstraction reaction of the benzophenone triplet (BPT) from SDS, which reduces Ag+ ions. It is found that the yield of colloidal Ag nanoparticle formation decreases remarkably with increasing concentration of Ag+ ions, indicating the efficient quenching process of BPT by Ag+ ions. Rate constants for the oxidation of BPK as well as the quenching of BPT by Ag+ ions in SDS micellar solution are considerably larger than those expected in the bulk solution, reflecting that Ag+ ions and BP molecules are concentrated in the SDS micelles. The rate of colloidal Ag nanoparticle formation, VAg, and BP photobleach, VBP, under steady-state irradiation with near-UV light (λ = 365 nm) were evaluated and the dependence of VAg and VBP on the concentration of Ag+ ions is interpreted quantitatively in terms of rate constants estimated by laser flash photolysis.